The present invention relates to twist-off closures for bottles and other containers and is particularly directed to a tamper-evident closure which will provide a readily discernable indication that the container has previously been opened. In the past, a wide variety of closure constructions have been proposed to seal the tops of bottles and other containers. Some of these closure constructions have also been designed to provide an indication that the closure has been opened in order to provide protection against tampering with the container's contents. The intent of these closures is to prevent the practice of removing the closure, introducing a contaminant into the container's contents, and replacing the closure.
Among the tamper evident closures which have been proposed in the past, some depend upon the fact that the closure is deformed during removal. For example, Sharp U.S. Pat. Nos. 1,796,728 and 1,796,729, disclose caps for bottles in which the caps when originally placed on the bottles have a beaded configuration which is changed to a relatively planar surface when the cap is removed. A different approach is exemplified by Amabili U.S. Pat. No. 4,055,266. This patent discloses a twist-off cap incorporating one or more flanges, which are turned under a bead on the bottle. These flanges are provided with a series of lines of weakening so that as the cap is removed the flanges are distorted and either rupture or separate along the lines of weakening to provide a visual indication that the cap has been removed.
Each of these prior art closures constructions has been subject to one or more serious defects. For example, the deformable closures of the type shown in the Sharp patent can be reapplied to a bottle and caused to assume a shape close enough to the original shape that a casual consumer may not notice that the bottle had previously been open. Other proposed closures have been too complex or too cumbersome or incompatible with high speed capping equipment to prevent their adoption for use with soft drink, beer bottles and the like.
A completely different approach to providing a tamper evident closure is disclosed in my earlier U.S. Pat. No. 4,782,969 for "Twist-off Bottle Caps". The cap disclosed in that patent includes a flat top and a ribbed skirt which carries along its lower edge a plurality of narrow tabs. During the capping process, these tabs are bent upwardly and inwardly into engagement with a plurality of ribs formed on the neck of the container immediately below an endwise lip formed thereon. When in the sealed and locked position, the portions of these tabs in engagement with the ribs are in compression and serve to hold the cap tightly sealed against the end of the lip. The cap is removed by first twisting it, causing the tabs to be cammed outwardly by the ribs to a position in which they are free of the ribs, and then lifting the cap from the neck of the bottle. The cap cannot, as a practical matter, be used to reseal the bottle since in the absence of some extremely complex mechanism there is no way in which the tabs can be forced inwardly to a position in which they reengage the ribs surrounding the neck of the bottle. While the closure construction shown in my earlier patent is effective to provide a tight closure for the container and to prevent undetected tampering with the container's contents, the closure is subject to the defect that for some intended uses an undesirably high amount of force is required to twist off the cap.